Impact absorbing means for marine propulsion



R. T. LARSEN 3,151,597

IMPACT ABSORBING MEANS FOR MARINE PROPULSION Oct. 6, 1964 Filed July 30, 1962 H 1E HE INVENTOR. faizzr I Lara/vlrraxwzfr,

United States Patent 3,151,597 IMPACT ABSGRBIWG RdEAWS FOR MARENE PROPULSIUN Robert T. Larsen, Menomonee Falls, Wis, assignor to Outboard Marine Corporation, Waukegan, 11L, :1 corporation of Delaware Filed July 38, N62, Ser- No. 213,242 13 Ciaims. (Cl. 115-41) The invention relates to marine propulsion apparatus, such as, for example, outboard motors and stern drive units. More particularly, the invention relates to structures which carry the propeller, which are normally submerged during operation, and which are accordingly subject to impact against a submerged obstacle.

Outboard motors and stern drive units both commonly include a strut or housing to which there is unitarily connected a lower unit which generally constitutes a streamlined gear box and journals a propeller-carrying shaft. The unitary structure or assembly of the strut and lower unit is generally carried on a hor zontal axis to permit upward vertical swinging of the unitary assembly out of the water in response to striking of a submerged obstacle.

Such striking of submerged obstacles results in impact loading of the unitary assembly and a change in the direction of momentum of the unitary assembly evidenced by the upward swinging of the unitary assembly about its horizontal pivotal mounting. Particularly in larger motors, shock absorbing devices have been employed to arrest the upward swinging of the unitary assembly by absorbing the associated kinetic energy.

However, such impacts often produce substantial forces which induce stresses and strains in the structural members, often damaging such members. With the advent of larger and heavier motors and increased speeds, this problem has become aggravated.

The invention involves the provision of bumper means including a body of resilient material for extending the time interval during which impact occurs, thereby reducing the magnitude of the resultant impact force, and thereby also protecting the unitary assembly. To the extent that the resilient bumper body is elasticaHy displaced, there is also obtained some conversion of energy into potential energy. The invention contemplates embedding in the resilient bumper body one or more nonresilient or rigid members or elements which inelastically deform under an impact of sufficient magnitude, either by bending or rupture. Such bending or rupture is effected through the transformation of energy into work, thereby substantially lessening the load on the shock absorbing system if one is provided. In addition, such bending or rupture permits increased penetration into the resilient material of the bumper means, thereby extending the time interval of impact and consequently reducing the magnitude of the impact force transmitted to the unitary assembly of the strut and lower unit.

In one preferred embodiment, a conical shaped bumper is detachably mounted to the forward end of a cigarshaped portion of the lower unit and incorporates a body of resilient material incorporating one or more metallic rings which are isolated from the lower unit by the resilient material in the bumper body. When the conical bumper hits a submerged object, the accompanying derangement of the resilient material, coupled with the resulting force acting in the resilient material, tends to rupture the metallic ring and to fragmentarily displace it outwardly of the axis of the conical structure. The detachable connection of the bumper body to the lower unit permits replacement of damaged or destroyed bumpers.

In another preferred form of the invention, the bumper is provided by an elongated resilient body which is carried on the front of the unitary assembly to provide either a generally vertical, resilient leading edge or a resilient leading edge which is inclined downwardly and rearwardly. The bumper body is detachably mounted to the unitary assembly and includes therein one or more rigid elements which are insulated from the unitary assembly and which will deform in response to an impact of such magnitude that would otherwise cause structural damage to the unitary assembly.

Other objects and advantages of the invention will become known by reference to the following description and the accompanying drawings wherein:

FIGURE 1 is a somewhat diagrammatic elevational view of an outboard motor incorporating various of the features of the invention;

FIGURE 2 is an enlarged view, partially broken away and in section, of a portion of the motor shown in FIG- URE 1;

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a somewhat diagrammatic, elevational view of a stern drive unit embodying various of the features of the invention;

FIGURE 5 is an enlarged view of a portion of the stern drive unit shown in FIGURE 4; and

FIGURE 6 is a sectional view taken along line 65 of FIGURE 5.

The outboard motor 11 shown in FIGURE 1 is representative of various types of outboard motors in which the invention can be incorporated. The motor 11 conventionally includes a transom bracket 13 which carries, on a horizontal pivot, a swivel bracket 15. Carried by the swivel bracket 15 on a vertical pivot is a unitary propulsion unit 17 including a power head 19 and a lower unit 21 which is submerged in water during normal operation and which includes a gear box portion 22. Unitarily connecting the power head 19 and lower unit 21 is a strut or housing 23. As is also conventional, within the gear box portion 22 there is rotatively supported a propeller shaft 25 mounting a propeller 27. Connecting the propeller shaft 25 to the power head 19 is power transmission means 2 including a driveshaft 31 extending into the lower unit 21 through the strut 23. In addition, suitable means, not material to the invention, can be employed for reversing the rotational direction of the propeller shaft.

As shown in FIGURE 1, in order to decrease resistance to travel through the water, the gear box portion 22 of the lower unit 21 is commonly stream-lined in cigar form, and extends forwardly of the leading edge of the strut. In accordance with the invention, the gear box portion 22 includes, at its forward end or nose, a bumper or resilient means 35 which serves to extend the impact time interval, thereby reducing the magnitude of the impact force transmitted to the lower unit and to convert or dissipate impact energy into work.

The time interval of impact is initially increased by forming the bumper 35 with a body 37 of resilient material, such as rubber or like material, which material deforms incident to striking thereof, thereby retaining forcetransmitting-engagement with the striking object over a greater period of time than if the bumper were rigid. In addition, each resilient deformation serves to absorb or convert some energy into potential energy which subsequently tends to restore the resilient material to its initial formation.

In order to provide both increased protection for the lower unit against damage resulting from high impact loading by further increasing the time interval of impact, and to dissipate energy by conversion thereof into Work, the resilient bumper body 37 is provided with rigid inserts or elements 39 (see especially FIGURES 2 and 3) magnitude of the impact force transmitted to the lower unit'21, and additionally causing conversion or dissipation of energy into work during the fracture or rupture of the rigid elements 39. Specifically, in the construction shown in FIGURES 1 and 2, the rigid inserts 39 take the form of a series of annular elements or rings 41 which are concentrically located in parallel relation toone another within the bumper body 37. Preferably, the rings 41 are wholly embedded in' the resilient body 37 of the bumper 35. However, if desired, the bumper can be fabricated as a laminar ineluding resilient, preferably non-compressible, laminae bonded to. one or more rigid elements. As shown best in FIGURE 2, the bumper 35 includes a mounting plate 43 which is bonded to the remainder of the bumper body 37 and is provided with a threaded stud 45 to facilitate attachrnent and replacement of the bumper body 37 on the lower unit 22. The mounting plate 43 is preferably isolated or insulated from the adjacent ring 41 by the resilient material of the'body 37 In operation, when the bumper body 37 is struck by an object at such speed as would otherwise damagethe lower a unit 22, the resilient material'of the bumper body 37 tends to crowd into the cores of the rings 41, thereby inducing radially outwardly directed stresses in the annular rings 41. Such stresses serve to fracture one or more rings 41, displacing the fractured ring segments outwardly. Such fracture of the ring elements 41 and accompanying deformation of the resilient material serves, as already explained, to convert energy to work and to lengthen the impact time interval by permitting increased penetration into the bumper body 37 of the impacting object.

Bonding of the rings 41 to the resilient material of the body 37 serves to unify the conical bumper 35. As beforementioned, it is preferred that the rings 41 be wholly embedded within the bumper body so that, even though the rings may be fractured due to impact loading, .the bond between the rings 41 and the resilient bumper material will more eliectively serve to retain the ring segments in assembled relation to the bumper body and prevent a shrapnel effect.

In FIGURES 4, 5, and 6, there is shown another bumper arrangement which is incorporated in a stern 'drive unit 111. and is particularly adapted to prevent hooking of a lower unit by submerged objects which strike the lower unit above the tip of a conical shaped, gear box nose. Specifically, the lower unit 113, shown in FIGURE 4, is one component of the stern drive unitlllwhich is conventionally fabricated except for the construction of the lower unit leading edge. As is conventional, the lower unit 113 is mounted about a horizontal pivot 114 for swinging movement through a vertical arc in response to striking of the lower unit 113 by a submerged object.

Moreparticularly, in the'construction shown in FIG- URES 4, 5, and 6, the lower unit includes a bumper 115 having a forward or leading edge 117 which is either vertical or is inclined downwardly and rearwardly to provide for free travel of an impacting object therealong as the lower unit 113 pivots upwardly. The bumper 115 includes a bumper body 119' which is generally formed so as to provide the leading edge 117 of the lower unit 113 with a rounded stream-lined configuration in horizontal section, as seen in FIGURE 6. The bumper body 119 is fabricated primarily of resilient, preferably non-compressible, material, such as rubber or rubber-like material, and is preferably bonded to a mount:

lengthening the time interval of impact and decreasing the 7 ing plate 121 which, in turn, can be detachably secured to the forward end of the lower unit 113 by suitable means, such as the bolts or screws 123.

Embedded in the bumper body 119 in forwardly spaced.

relation from the mounting plate 121 are a pair of vertically elongated rigid inserts, elements or plates 125. The plates 125 are disposed in spaced planes parallel to the fore and aft center line of the lower unit 113. ;As a

result, striking of the bumper 115 by an object of suflicient size and at suflicient speed, tends to crowd the resilient bumper body material between the plates 125, thereby tending to bend the plates apart from each other. Such bending permits increased penetration of the bumper body 119 by the impacting object, with accompanying In summary, both bumper bodies 39 andll? are constructed with relatively rigid inserts which deform inelastically under sufiiciently high loading so as'to protect the remainder of the lower unit from impact forces which could otherwise cause serious damage. In addition, both bumper bodies serve to store some impact energy as potential energy in the resilient body material, The detachable mounting of the bumper on the lower unit allows easy replacement of fractured or, damaged bumpers.

Various of the features of the invention are set forth in the following claims. What is claimed is:

1. In a marine propulsion device including a vertically 1 tiltable unitary structure including a strut and a lower unit, said unitary structure being provided with a forwardly located bumper having a body of resilient material, the improvement wherein said bumper includes relatively immovable rigid insert means located in said resilient material for inelastic derangement in respouse to receipt of impact loads transmitted through said resilient material.

2. A device in accordance with claim 1 wherein said bumper'includes means for detachable connection with said unitary structure.

3. A device in accordance with claim 2 wherein said insert means is insulated from said unitary structure and from said connecting means by said resilient material.

4. In a marine propulsion device having a vertically tiltable lower unit with a generally cigarshaped gear box portion including a conically shaped bumper at the forward end thereof incorporating a bumper body of resilient material, the improvement wherein said bumper includes relatively rigid annular means in said'resilient material for derangement in response to receipt of impact loads transmitted through said resilient material, said annular means being wholly supported by said resilient material.

5. A device in accordance with claim 4 wherein said bumper includes mounting means for detachably mounting said bumper to the front of said gear box portion, and

said resilient material is interposed between said mounting means and said rigid insert means, and between said gear box portion and said rigid means, to prevent direct transmission of force therebctween.

6. In a marine propulsion device, the. combination of a vertically tiltable lower unit with a generally cigarshaped gear box portion including a conically shaped bumper at the forward end thereof incorporating a bumper body of resilient material and relativelyrigid annular means in said resilient material for derangement in response to receipt of impact loads transmitted through said resilient material,

said rigid means comprising a'plurality of spaced rings disposed in concentric relation to the axis of said conically shaped bumper.

7. A device in accordance with claim 6 wherein said rings are of metal.

8. in a marine propulsion device including a vertically tiltable unitary structure including a strut and a lower unit, and a bumper at the forward end of said unitary structure, said bumper having a body of resilient material, the improvement wherein said bumper has a leading edge which is free of upward and rearward incline, and

relatively immovable rigid means is in said resilient material for inelastic derangement in response to receipt of impact loads transmitted through said resilient material.

9. A device in accordance with claim 8 wherein said relatively rigid means comprises a pair of spaced plate elements disposed in evenly spaced parallel relation to the fore and aft center line of said unitary structure, and

resilient material disposed, in part, between said unitary structure and said plate elements to prevent direct transmission of force therebetween.

10. A device in accordance with claim 9 wherein said bumper includes mounting means for detachable connection of said bumper to said unitary assembly, and

said resilient material is interposed between said plate elements and said mounting means to prevent direct transmission of force therebetween.

11. A device in accordance with claim 9 wherein said plate elements are of metal, and

said bumper has a forwardly convex horizontal cross section.

5 12. A marine propulsion device including a vertically tiltable unitary structure including a lower unit and a strut, and bumper means detachably connected to the forward edge of said unitary structure and including a bumper body formed of resilient material and a relatively rigid insert embedded in said resilient material in spaced relation to said unitary structure and free of any connection with said unitary structure except through said resilient material, said insert being inelastically deformable in response to transmission through said resilient material to said insert of forces of such magnitude as might cause structural damage to said unitary structure. 13. In a marine propulsion device including a vertically tiltable lower unit provided with a forwardly located bumper, the improvement wherein said bumper comprises a bumper body of resilient material, and a relatively rigid immovable insert located in said resilient material for inelastic derangement in response to receipt of impact loads transmitted through said resilient material.

References Cited in the file of this patent UNITED STATES PATENTS 1,943,288 Chandler Jan. 16, 1934 2,776,695 Wells Jan. 8, 1957 2,998,214 Peterman Aug. 29, 1961 3,056,620 Adams Oct. 2, 1962 

1. IN A MARINE PROPULSION DEVICE INCLUDING A VERTICALLY TILTABLE UNITARY STRUCTURE INCLUDING A STRUT AND A LOWER UNIT, SAID UNITARY STRUCTURE BEING PROVIDED WITH A FORWARDLY LOCATED BUMPER HAVING A BODY OF RESILIENT MATERIAL, THE IMPROVEMENT WHEREIN SAID BUMPER INCLUDES RELATIVELY IMMOVABLE RIGID INSERT MEANS LOCATED IN SAID RESILIENT MATERIAL FOR INELASTIC DERANGEMENT IN RESPONSE TO RECEIPT OF IMPACT LOADS TRANSMITTED THROUGH SAID RESILIENT MATERIAL. 